Abortive initiation is an early process of genetic transcription in which RNA polymerase binds to a DNA promoter and enters into cycles of synthesis of short (truncated) mRNA transcripts that are released before the transcription complex disassociates from the promotor. The truncated RNA transcripts cannot be converted to full-length transcripts by RNA polymerase and become by-product that accumulates during the course of transcription. This process occurs in both eukaryotes and prokaryotes. Abortive initiation is typically studied in the T3 and T7 RNA polymerases in bacteriophages and in Escherichia coli.
Abortive initiation is a normal process of transcription and occurs both in vitro and in vivo. After each nucleotide-addition step in initial transcription, RNA polymerase, stochastically, can proceed on the pathway toward promoter escape (productive initiation) or can release the RNA product (transcript) and revert to the RNA polymerase-promoter open complex (abortive initiation). During this early stage of transcription, RNA polymerase enters a phase during which dissociation of the transcription complex energetically competes with the elongation process.